As a result of the development of gallium nitride based LEDs (GaN-LEDs) that emit blue light, utilization of LEDs as illumination devices have recently been the focus of attention. When used as an illumination device, gallium nitride based LEDs have a variety of properties, such as (a) the life of elements is long, almost infinite for practical use, (b) energy efficiency is high, and little heat is released, (c) luminosity is high, (d) light controlling properties are excellent (a desired tone of color can be generated), and (e) the size of a single element is very small, making it possible to mount elements in a desired form, as compared to conventional illumination devices, such as incandescent light bulbs and fluorescent lamps.
It is desirable for white light to be gained in order to use LEDs as light sources. In recent years, a white light source (white LEDs) has been implemented by covering a GaN-LED with an yttrium aluminum garnet fluorescent thin film, and therefore, it can be expected that LED illumination devices will be more widely used in the future.
It is necessary to make LED illumination devices easy to handle in the same manner as conventional electric lamps and fluorescent lamps, in order for LED illumination devices to gain widespread in household use. For example, though LEDs have a life that is longer than that of conventional light bulbs and fluorescent tubes, still, in some cases, it becomes necessary to change them in general homes. Therefore, it is desirable for the attachment and removal of LED light sources (which corresponds to light bulbs and fluorescent tubes) to and from illumination devices to be able to be carried out in the same manner as or more easily than conventional electric lamps and the like.
However, such LED illumination devices where attachment and removal of an LED light source can be easily carried out have not been researched.
In addition, it is necessary to solve the problem where the temperature of LED chips increases when supplied with a large amount of power, as described below, when LEDs are used for an illumination device.
At present, the intensity of light flux that is gained from a white LED, as described above, is several lm (lumen) when the LED is in bullet form (having a diameter of 3 mm), and is several tens of lm when the LED is of a large area type with high brightness. However, it is necessary to gain light flux of 1000 to several thousands of lm from such a white LED, in order for the white LED to be used as a light source for a liquid crystal projector or a light source for the headlights of an automobile. In order to achieve this, it is necessary to supply power of 20 W to 100 W or greater to the white LED, because the light emitting efficiency of white LEDs at present is approximately 25 (lm/W) at the maximum when the white LED is of a type that is currently in use, and approximately 50 (lm/W) at the maximum when the white LED is of a type that is prepared in a laboratory.
In the case where such a large amount of power is supplied to a presumably small mounting region for a light source as that described above, there is a risk that the LED chip may store heat and the temperature may increase. In addition, even in the case where this heat is conveyed to the substrate on which the LED chip is mounted, this substrate stores heat, which increases the temperature, and thereby, there is a risk that the temperature of the LED chip may also increase. LEDs are semiconductor devices, and therefore, the higher the temperature becomes, the higher the probability of occurrence of non-radiative recombination becomes, reducing the light emitting efficiency. Accordingly, it is necessary to appropriately release heat generated in an LED chip to the outside so as to prevent the temperature of the LED chip from excessively increasing, in order to make an LED illumination device emit a large amount of light efficiently.
Japanese Unexamined Patent Publication No. 2002-232009 describes the release of heat from the surface of a conductive pattern for supplying power to LEDs which are provided on a flexible substrate (see [0050] and FIG. 4), and the release of heat from a fin for heat release made of a silicone resin which is provided on the rear surface of a flexible substrate (see [0046] and FIG. 8). Here, concerning the material of the flexible substrate, there is a description “flexible resin member” in [0032]. Therefore, the function of a substrate in the release of heat has not yet been sufficiently looked into.
Meanwhile, the present inventors have proposed that an LED chip be mounted on a diamond substrate (or a substrate of which the surface is covered with diamond or diamond carbon) in order to convey to the outside heat that has been generated in the LED chip, in Japanese Unexamined Patent Publication No. 2002-329896 (see [0020] and FIG. 3). The thermal conductivity of diamond at room temperature is approximately 20 W/cmK, which is higher than that of a substrate that is conventionally used to mount an LED chip (sapphire, quartz, SiC, GaN, AlN or the like) by one digit to two digits. Therefore, the heat that is generated in an LED chip is absorbed by the diamond substrate so that an increase in the temperature of the LED chip can be restricted.
The substrate for mounting an LED chip is as thin as several mm, so that the space for installment can be made small. Therefore, heat from the LED chip tends to be stored in the substrate. In Japanese Unexamined Patent Publication No. 2002-329896, the heat that is absorbed by the diamond substrate is “released to the outside from the bottom and the sides” of the substrate ([0020]). However, in the case where the density of installment of LEDs is further increased, release of heat from the substrate to the surrounding air becomes insufficient, making the temperature of the substrate increase. Therefore, there is a risk that the heat generated in an LED chip may not be appropriately released.
The present invention is provided in order to solve such problems, and an object thereof is to provide an LED illumination system where an LED light source can be easily attached and removed. Another purpose of the present invention is to allow such an LED illumination system to appropriately release the heat that is generated in LEDs to the outside of the system.